A variety of sensors have been developed for detecting different gaseous combustion emission components. Examples of the different gaseous components which these sensors can detect include, but are not limited to oxygen (O.sub.2), carbon monoxide (CO), carbon dioxide (CO.sub.2), hydrocarbons (HC), and nitrogen oxides (NO.sub.x). These sensors can be used in a variety of devices including, for example, automotive engines, diesel engines, gas turbine engines, jet engines, power plants, furnaces, and barbecues. Many of these gaseous components are hazardous.
Information derived from these sensors can be used for a variety of purposes. Data from the sensors can be used for the feedback control of different aspects of a device which is producing a gaseous emission. Alternatively, these sensors can simply be used to monitor the content of the emission. For example, these sensors can be used as a component of an on-board, OEM emissions control system for an automotive engine or as an off-board emissions measuring device used for inspection and maintenance, for example as a tool for an automotive mechanic.
A need exists for sensors which can detect a wide array of gaseous components. For example, a need exists for a sensor which can determine the concentrations of oxygen, carbon monoxide, carbon dioxide, hydrocarbons, and nitrogen oxides in a sample. The sensors should have a high signal-to-noise ratio and thus be able to accurately determine the concentrations of various components of a gaseous sample. The sensors should be simple, reliable, and inexpensive to manufacture. These and other objectives are provided by the sensors, devices, and methods of the present invention.